JP3497177B2 - Method for producing porous membrane surface-modified with perfluorocarbon copolymer - Google Patents

Abstract

A process is provided for producing a porous membrane product comprising a porous membrane having its surface completely modified with a perfluorocarbon copolymer composition. The porous membrane substrate is contacted with a solution containing a perfluorocarbon copolymer composition to bind the composition onto the substrate surface. The substrate is subjected to a mechanical force to remove excess perfluorocarbon copolymer composition and then is heat treated.

Description

Description: FIELD OF THE INVENTION The present invention relates to a thin porous membrane having a surface modified with a perfluorocarbon copolymer composition, and a method for producing the membrane.

Background of the Prior Art Porous membrane filters have been utilized in a variety of environments to separate substances in fluid streams. The membrane is formed from a fixed polymer matrix and has a high degree of precision controlled and measurable porosity, pore size, and thickness. In use, membrane filters are generally incorporated into devices such as cartridges and are adapted for insertion into a fluid stream for removal of particles, microorganisms or solutes from liquids and gases.

To be useful, the membrane filter must be resistant to the fluids it is trying to filter so as to maintain its strength, porosity, chemical integrity and cleanliness. For example, in the manufacture of microelectronic circuits, membrane filters are widely used to purify various process fluids to prevent contaminants from damaging the circuit. Filtration or purification of the fluid is carried out by passing the process fluid through a membrane filter under a pressure differential across the membrane, which forms a higher pressure zone upstream of the membrane than downstream. Is normal. Thus, the liquid filtered in this manner experiences a pressure drop across the membrane filter. This pressure difference also results in a liquid having a higher dissolved gas level on the upstream side than the downstream liquid. This results from the fact that gases such as air have a higher solubility in liquids at higher pressures than liquids at lower pressures. As the liquid passes from the upstream side of the membrane filter to the downstream side, dissolved gas emerges from the solution at the membrane, leading to gas evolution of the liquid. Also, gassing of liquids can occur spontaneously without pressure differential as long as the liquid contains dissolved gas, and the driving force for the gas to come out of solution, for example on the surface of the membrane. There are nucleation sites where gas pockets can form and grow. Gas-generating liquids typically used in the manufacture of semiconductors and microelectronic devices are waters of extremely high purity, ozonated water, organic solvents such as alcohols, and rich and aqueous solutions that can contain oxidants. It will usually include others that are generally significantly more chemically active, such as acids or bases. These chemically active fluids require the use of chemically inert filters to prevent degradation of the membranes, which can lead to chemical destruction of the membrane composition, which usually results in The purity of the fluid that results in the extractable substance being shed from the filter, thus filtering
Compromise integrity and cleanliness. In these applications, fluorocarbon substrate membrane filters made from fluorine containing polymers such as polytetrafluoroethylene are commonly used. Fluorine-containing polymers are well known for their chemical inertness or excellent resistance to chemical attack. One disadvantage of fluorine-containing polymers is that they are hydrophobic and therefore membranes made from such polymers are wetted with aqueous or other liquids that have a surface tension greater than the surface energy of the membrane. It is difficult. Another problem often encountered during the filtration of gas-generating liquids with hydrophobic membrane filters is that the membrane provides nucleation sites for the dissolved gas to come out of solution under the driving force of differential pressure during the filtration process. Is Rukoto. Gases that come out of solution at these nucleation sites on the hydrophobic membrane surface, including the inner pore surface and the outer or geometric surface, form gas pockets that attach to the membrane. As these gas pockets grow in size due to continued outgassing, they begin to displace liquid from the pores of the membrane, eventually reducing the effective filtration area of the membrane. This phenomenon is commonly referred to as dewetting of the membrane filter. For, the fluid-wet or fluid-filled portion of the membrane is gradually converted to a fluid-non-wet or gas-filled portion. Also, dewetting of the membrane can occur naturally when a wetting membrane, such as a hydrophobic membrane moistened with an aqueous fluid, is exposed to a gas, such as air.
It has been found that this dewetting phenomenon occurs more frequently and is more pronounced in fluorocarbon substrate membranes made from fluorine containing polymers such as polytetrafluoroethylene. It has also been found that the rate at which dewetting occurs is faster for small pore size membranes, such as 0.2 microns or less, than for larger pore size membranes. During the filtration process, reducing the effective membrane area available for filtration by dewetting of the membrane in the filter device results in a reduction in the overall filtration efficiency of the filter. This decrease in efficiency becomes manifest in a decrease in the flow rate of fluid through the filter at a given pressure drop, or an increase in pressure drop at a given flow rate. Thus, as the membrane filter dewets over time, the user cannot purify or filter the same volume (per unit time) of process liquid as when the filter was newly installed and therefore completely wet. . This reduction in total throughput of the filtration process results in increased user time and cost to purify unit volumes of process liquid. Faced with reduced throughput, users are often required to install new filters and discard dewetting filters in the process. This premature filter change due to dewetting, not necessarily due to depletion of the filter's ability to hold debris, results in unplanned downtime and increases the total cost to the user. Optionally, the user makes adjustments to other elements of the filtration system, such as increasing the rate at which the pump forces the fluid through the filter to increase the pressure drop across the membrane, thus providing a constant The decrease in efficiency can be compensated by maintaining the flow rate of. These adjustments also add work costs to the user,
And it increases the likelihood of failure of other elements in the system, as well as the potential for process liquid leakage due to increased process pressure. Another option for the user to avoid premature filter changes due to dewetting is to treat the filter to rewet the membrane. This process is time consuming as it requires removing the filter device from the filtration system, resulting in unplanned downtime, and results in the introduction of contaminants derived from the rewet process to the process liquid passing through the filter. There is often a possibility. Typically, alcohols such as isopropanol (these are
Low surface tension rewetting agents can be used, including those that are flammable liquids and pose a safety hazard. Before returning the filtration device to use, the end user re-wets the dewetting filter with alcohol, then flushing with water and then flushing with the process liquid. Although membrane manufacturers may have the expertise to handle and process dewetting filters, the end user has the ability or desire to perform such additional costly process steps. May not do.

All membranes are characterized by their nominal pore size, which is directly related to the particle retention properties of the membrane. Pore size is directly proportional to flow rate through the membrane, and particle retention is inversely proportional. It is desirable to maximize both particle retention and flow rate. Significantly increasing one of these properties and significantly decreasing the other of these properties is undesirable.

U.S. Pat. No. 4,470,859 to Venezuela et al. Discloses that the surface of a microporous substrate formed of a fluorocarbon such as polytetrafluoroethylene is modified by coating the copolymer with a solution of a perfluorocarbon copolymer. To make the surface of the membrane more water wettable. The perfluorocarbon copolymer is dissolved in the solvent at elevated temperature. The membrane is then immersed in the solution and placed in a vacuum chamber. The pressure in the chamber is then reduced to about 150 mmHg (absolute pressure) to remove air from the filter. After that, the pressure in the room
It is quickly returned to atmospheric pressure. This coating process is repeated to ensure that what has been described by Venezla et al. As complete solution penetration into the pores of the membrane. By proceeding in this manner, the membrane surface and inner walls that define the interstices in the membrane are coated with a perfluorocarbon copolymer. After the coating process,
The solvent is removed by evaporation using heat and vacuum, or the solvated perfluorocarbon copolymer is precipitated with the material at which the copolymer is completely insoluble. Solvents used to form the solution include halocarbon oils, perfluorooctanoic acid, decafluorobiphenyl, N-butylacetamide and N, N-dimethylacetamide. Following modification of the membrane surface, Venezla et al. Teach avoiding the use of a fluid containing solvent for the modifying copolymer on the membrane surface. Also,
Benezula et al. Disclose that alcoholic solutions of polymers should be avoided.

U.S. Pat. -Methyl-8-nonenoate) or perfluorinated (3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) copolymers, and methods of forming solutions of perfluorinated ion exchange polymers are disclosed. Has been done. The perfluorinated ion exchange polymer is dissolved in an alcohol solvent such as isopropanol at elevated temperature and pressure. The resulting solution is a catalyst support used in promoting various chemical reactions to produce and repair films and non-porous membranes used in electrolysis processes such as electrolysis of aqueous sodium chloride. For coating substrates such as, for coating porous diaphragms and converting them into non-porous products, and for reusing spent perfluorinated polymers having sulfonic acid or sulfonate functional groups. It is described as being useful for recovery. In electrolytic processes such as those disclosed by these patents, the extractables from the coated diaphragm are not a substantial issue, and the porosity of the modified diaphragm is not critical.

Also, U.S. Pat. No. 4,348,310 discloses a solution of a fluoropolymer containing sulfonyl fluoride. The solvent used here is a fully halogenated saturated hydrocarbon, preferably having at least one terminal sulfonyl fluoride polar group. The solution is said to be used to repair holes in membranes made from fluorinated polymers and to make ion exchange film membranes, dialysis membranes, ultrafiltration membranes and microfiltration membranes. ing. Other disclosed uses for these solutions are electrolysis by contacting the solution with a diaphragm and then evaporating the halogenated solvent and then hydrolyzing the coated diaphragm to convert the sulfonyl fluoride group to the acid or salt form. Coating a porous diaphragm for a chemical cell.

US Pat. No. 4,902,308 to Mallouk et al. Also describes a method of modifying the surface of a porous, expanded polytetrafluoroethylene membrane with a polymer of a solution of a perfluorocation exchange polymer. Also, Mallouk et al. Teach that contacting the surface modified membrane with a fluid containing a solvent for the polymer should be avoided.

U.S. Pat. Nos. 4,259,226 and 4,327,010 disclose modifying the surface of a porous membrane with a fluorinated polymer having a carboxylate group. No process steps are disclosed to control the extractables from the membrane or to control the degree of binding of the modifying composition to the membrane surface.

U.S. Pat. ing. The modifying polymer composition can contain a surfactant and may contain excess modifying composition, both of which are sources of unwanted extractables. In addition, these patents are greater than 0.25 mm and preferably about 0.76.
A method of coating a thick polyfluorocarbon diaphragm having a thickness of mm to about 5.0 mm with a perfluoroion exchange polymer is disclosed. Thin membrane substrates are specifically excluded as being the use of perfluor ion exchange polymer coatings having equivalent weights greater than 1000.

Therefore, it would be desirable to provide thin porous membranes with modified surfaces that improve wettability. In addition, it would be desirable to provide such membranes that are resistant to chemical attack, such as porous membranes composed of fluorine-containing polymers. Further, it would be desirable to provide such a membrane that does not aid in gas nucleation on the surface when filtering the gas generating fluid so that it will not dewet during use. It would also be desirable to provide such membranes with improved particle retention properties compared to unmodified membranes without significantly adversely affecting the bundle properties of the resulting membranes, especially those with small pore sizes. .

SUMMARY OF THE INVENTION The present invention is directed to a thin porous polymer membrane substrate that has been fully modified, including internal pore surfaces and external geometric surfaces, with attached and bonded perfluorocarbon copolymer compositions. It provides a manufacturing method. The perfluorocarbon copolymer composition is deposited in such a way that it is bonded to the polymer substrate surface. The solution of the perfluorocarbon copolymer composition depends on immersing the polymer substrate in the solution, or by passing the solution through the polymer substrate under pressure, or by penetrating the pores of the membrane under pressure. It is thus contacted with the polymer substrate. As used herein, the term "solution" refers to
It refers to a liquid composition containing a completely and / or partially dissolved perfluorocarbon copolymer composition in a solvent, diluent or dispersion medium. These solutions comprise a suspension of undissolved perfluorocarbon copolymer composition suspended in a dispersion medium. The solution comprises a liquid composition that is a solvent, diluent or dispersant medium for the perfluorocarbon copolymer composition that completely wets the membrane substrate, or it When not wet, the membrane is pre-wet so that the solution can enter the pores of the membrane or the solution can be forced into the pores. It is a requirement that the solution completely enter the pores of the membrane. The surface-modified membrane substrate is then subjected to mechanical forces to selectively remove excess unbound perfluorocarbon copolymer composition and distribute it over the surface of the substrate.

In another embodiment, the unbound perfluorocarbon copolymer composition is applied to the surface that was previously subjected to mechanical forces while avoiding the removal of the perfluorocarbon copolymer composition bound to the membrane substrate. A step of contacting a solvent, diluent or dispersant that is selectively removed, such as by solvation or dilution, may be added. The resulting surface modified membrane is then dried and heat treated to improve the bond strength between the membrane substrate and the bound perfluorocarbon copolymer composition.

The heat-treated surface-modified membrane has its surface bound to a bound perfluorocarbon copolymer composition (which, surprisingly,
The unbound solvated perfluorocarbon copolymer composition is completely modified with a composition comprising a solvent or diluent that solvates and / or dilutes). When using the term "fully modified" herein, it is such that the extent of surface modification is such that dewetting of the membrane cannot be detected when the membrane is contacted with a gas generating liquid. Moreover, it means that the unstained portion of the film surface is not detected when the film is colored with methylene blue dye. Thus, excess or unbound perfluorocarbon copolymer composition can be selectively removed from the modified membrane without adversely affecting the modified membrane surface. In addition, the unbound perfluorocarbon copolymer composition can be removed from the membrane so that it is no longer a possible source of extractables that could be released in the fluid passing through the surface modified membrane. Thus, the heat-treated surface-modified membrane is substantially free of extractables, even when using a liquid that is a solvent or diluent for the unbound solvated perfluorocarbon copolymer composition. In addition, the surface modifying composition is tested by measuring the increase in pressure drop across the membrane during filtration of the purified water, in an amount and at a concentration such that the porous membrane substrate is not substantially closed or occluded. use. The modified porous membrane product of the present invention has substantially the same permeability as the unmodified porous membrane substrate as measured by pressure drop. That is, the increase in pressure drop for the modified porous membrane of the present invention as compared to the pressure drop across the unmodified porous membrane substrate is 25
It does not exceed%. This increase in pressure drop is preferably no more than 15%, and most preferably no more than 10% as compared to the pressure drop across the native porous membrane substrate.

Membranes modified according to the present invention can have the particle retention properties of unmodified membranes with much smaller pore sizes while substantially maintaining the bundle properties of the unmodified membranes. Furthermore, since the composition for surface modification of the membrane is formed from a perfluorocarbon copolymer composition, the modified surface is also highly resistant to chemical attack. In addition, the perfluorocarbon copolymer composition does not aid in gas nucleation at the surface of the membrane when filtering gas generating liquids. Thus, when filtering a gas-generating liquid, the useful life of the membrane is that of a native fluorocarbon membrane that aids in the nucleation of gas on the surface when filtering the gas-generating liquid that results in dewetting of the membrane. Significantly longer than useful life.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a plot showing the results of the standard dewetting test of Example 10.

FIG. 2 is a plot showing P / Q vs. drain number for the standard SC2 drain test of Example 11.

  FIG. 3 is an unstained control of Example 14 (4.3 ×).

  FIG. 4 is a diagram (4.3 ×) of the staining control of Example 14.

FIG. 5 is a diagram (4.3 ×) of the non-pre-wet precipitate coated control of Example 15 stained.

FIG. 6 is a diagram (4.3 ×) of the dyed pre-wet precipitate coated sample of Example 15.

FIG. 7 is a diagram (4.3 ×) of the dyed non-pre-wet coated sample of Example 14.

Figure 8 is a diagram of the pre-wet coated sample of Example 14 stained (4.
3x).

FIG. 9 is a diagram (4.3 ×) of a surface-modified membrane produced by the process of the invention discussed in Example 16 as dyed.

FIG. 10 is a diagram of a surface-modified membrane produced by the process of the present invention discussed in Dyeing Example 17.

DESCRIPTION OF SPECIFIC EMBODIMENTS The membrane surface modifying compositions of the present invention are such as those sold by DuPont under the tradename "NAFION" or by Asahi Glass under the tradename "FLEMION". Polymer compositions commonly known as various perfluorocarbon copolymers, which are attached to the membrane substrate.

These perfluorocarbon copolymers are generally copolymers of at least two monomers, and one monomer is vinyl fluoride, hexafluoropropylene, fluoropolymer. It is selected from the group of fluorine-containing monomers such as vinylidene, trifluoroethylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ethers), tetrafluoroethylene and mixtures thereof.

The second monomer is (SO ₂ F), (SO ₃ M), (SO ₃ R),
(SO ₂ NR ₂ ), (COF), (CO ₂ M), (CO ₂ R) or (C
ONR ₂ ) groups, where M is H, alkali metal, alkaline earth metal or NR ₄ , and each R is independently H, C
Alkyl or aryl groups such as H ₃ , C ₂ H ₅ or C ₆ H ₅ , which are optionally substituted with other functional groups such as hydroxyl, amine, ether or carbonyl groups and the like. Selected from the group of fluorine-containing monomers containing functional groups which can be alkyl groups or substituted aryl groups) or which can be converted into these.
Examples of such second monomers are generally of the formula CF ₂ = CFR _f −
It can be represented by X. R _f in the general formula is
A linear or branched difunctional perfluorinated group containing from 1 to 8 carbon atoms having any suitable or conventional shape, including those containing ether linkages, and having a carbon-carbon bond It is directly bonded to the vinyl group CF ₂ ═CF via an ether bond or preferably an ether bond. X in the general formula is (SO ₂ F), (SO ₃ M), (SO ₃ R), (SO ₂ N)
R ₂ ), (COF), (CO ₂ M), (CO ₂ R) or (CONR ₂ )
A group (where M is H, alkali metal, alkaline earth metal or NR ₄ and each R is independently H, CH ₃ , C ₂ H ₅
Or an alkyl or aryl group such as C ₆ H ₅ and which optionally contains other functional groups such as hydroxyl, amine, ether or carbonyl groups to form a substituted alkyl or substituted aryl group. Which may be formed) or a functional group which can be converted into these functional groups. One limitation in the general formula is the general requirement that there be at least one fluorine atom on the carbon atom adjacent to the -X group.

Typically, such second monomers containing sulfonyl fluoride groups that can be converted to sulfonyl-based ion exchange groups are described in U.S. Pat. The production method of is described in U.S. Pat. These perfluorocarbon copolymers typically have pendant SO ₂ F-based functional groups that can be converted to (SO ₃ M) groups. In one embodiment of the present invention, the surface modifying composition comprises pendant carbonyl-based functional groups that can be converted to carbonyl-based ion exchange groups.

Perfluorocarbon copolymers having pendant carbonyl-based ion-exchange functional groups are described in US Pat.
2 or can be prepared in any suitable conventional manner, such as according to JP 52-38486, or U.S. Pat.
Reference can be made to these references if necessary, as they can be polymerized from carbonyl functional group containing monomers derived from sulfonyl group containing monomers by methods such as those described in 051. Specific examples of the carbonyl fluoride-containing monomer include: Is mentioned. Preferred carbonyl-containing monomers include Is mentioned. Thus, preferred perfluoro carbon copolymer used in the present invention, wherein -OCF ₂ CF ₂ X '
And / or _{-OCF 2 CF 2 CF 2 Y-} B-YCF 2 CF 2 O- ( wherein,
X'is sulfonyl fluoride (SO ₂ F), carbonyl fluoride (CO
F), sulfonate methyl ester (SO ₃ CH _3), carboxylate ester (COOCH _3), ionic carboxylate (COO ^- Z ⁺⁾ or ionic sulfonate (SO ₃ ^-
Z ⁺ ) and Y is sulfonyl (SO ₂ ) or carbonyl (C
Is O), B is -O -, - O-O - , - S-S-, and wherein _{NH (CR 1 R 2) x} NH ( wherein, R ₁ and R ₂ are short-chain alkanes, alkenes, Di-) selected from hydrogen and amine groups
And polyamines, and Z is an alkali metal such as hydrogen, lithium, cesium, rubidium, potassium and sodium, or an alkaline earth metal such as barium, beryllium, magnesium, calcium, strontium and radium, or quaternary ammonium. Carbonyl and / or sulfonyl-based functional groups represented by (which are ionic).

The sulfonyl form of a perfluorocarbon copolymer is typically a polymer in which either a functional group or a pendant side chain having a functional group is attached to the fluorinated hydrocarbon backbone. Target. This pendant side chain is, for example, Group (wherein, R _'f is F, C1 or C ₁ -C ₁₀ perfluoroalkyl group, and W is F or C1, preferably a F) may contain. The functional group on the side group in the polymer is a terminal group which can be bonded to the side group via an ether bond. Would normally be present in. Examples of this type of perfluorocarbon copolymers are found in US Pat.
As disclosed in 0568 and 3718627, if necessary,
See them.

Additional examples of the general formula _{CF 2 = CF-T k -CF} 2 SO 2 F ( wherein
T is a difunctional fluorinated group containing 1 to 8 carbon atoms, and k is 0 or 1.). Substituent atoms at T include fluorine, chlorine or hydrogen. The most preferred perfluorocarbon copolymers are free of both carbon-bonded hydrogen and chlorine, ie they are perfluorinated because they are maximally stable in harsh environments. The T groups in the above formulas may be branched or unbranched or straight chain and may have one or more ether linkages. The vinyl group in this group of sulfonyl fluoride-containing comonomers is linked to the T group via an ether bond, ie the comonomer has the formula CF ₂ = CF-
It is preferred to have the _{O-T-CF 2 -SO 2} F. Examples of such sulfonyl fluoride containing comonomers include: Is.

The most preferred sulfonyl fluoride containing comonomer is perfluor (3,6-dioxa-4-methyl-7-octenesulfonyl fluoride), Is.

Sulfonyl-containing monomers are described in U.S. Pat.
References such as 17, 3718627, and 3560568 can be made if necessary.

A preferred group of perfluorocarbon copolymers for use in the present invention is the following repeating unit: [Wherein, h is 3 to 15, j is 1 to 10, p is 0, 1 or 2 and X ″ are taken together to form 4 fluorines or 3 fluorines and 1 Is chlorine, Y is F or CF ₃ , and R ′ _f is F, Cl or a C ₁ -C ₁₀ perfluoroalkyl group.

The method of the invention includes any copolymer containing sulfonyl or carbonyl based functional groups, including copolymers containing both sulfonyl and carbonyl type functional groups, and mixtures of copolymers with different functional groups. Perfluorocarbon copolymers can be used. The most preferred sulfonyl-containing perfluorocarbon copolymer is a copolymer of tetrafluoroethylene and perfluoro (3,6-dioxa-4-methyl-7-octenesulfonyl fluoride), and from this the sulfonic acid form Alternatively, the salt form can be obtained. The most preferred carbonyl-containing perfluorocarbon copolymer is tetrafluoroethylene and methylperfluoro (4,7-dioxa-5-
Copolymer with methyl-8-nonenoate) and from which the carboxylic acid or salt form can be obtained.

The sulfonyl, carbonyl, sulfonate and carboxylate esters, and sulfonyl and carbonyl based amide forms of perfluorocarbon copolymers are usually readily converted to the ion exchange form by a hydrolysis reaction. For example, the salt form can be obtained by treatment with a strong alkali such as NaOH, and the acid form can be obtained by treatment with an acid such as HCl. This conversion step can be carried out before or after surface treatment of the membrane substrate with the sulfonyl, carbonyl, sulfonate and carboxylate esters of the perfluorocarbon copolymer and sulfonyl and carbonyl-based amide forms.

The perfluorocarbon copolymer used in the method of the invention need not be limited to a specific equivalent weight, but instead,
Any copolymer having any equivalent weight is used unless it is bound to the surface of the membrane substrate and is substantially not removed by contact with the liquid composition which is the solvent or diluent for the unbound solvated copolymer. be able to. In addition, any perfluorocarbon copolymer having any equivalent weight to prevent dewetting during use of the resulting surface modified membrane can be used. The equivalent weight of the perfluorocarbon copolymer is typically about 900 to about 1500, and about 1050 to about 125.
0 is more common. The equivalent weight of perfluorocarbon copolymer is the average weight of one repeating unit in the copolymer.

Solvents used to form the perfluorocarbon copolymer solution from which the surface modification of the membrane substrate is derived include those disclosed by U.S. Pat. No. 4,386,987, which is referenced if necessary. These solvents are halocarbon oil, perfluorooctanoic acid oil,
Includes N-alkylacetamide and decafluorbiphenyl. Alternatively, the halogenated saturated hydrocarbons disclosed by U.S. Pat. No. 4,348,310 can be used, and should be referred to if necessary. Preferred solvents are the alcoholic solvents disclosed by US Pat. Nos. 4,430,382 and 4,453,991, which may be referred to if necessary. The alcohol solvent is methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, 2-methoxyethanol, 2-.
Includes ethoxyethanol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane and acetonitrile, as well as mixtures thereof or mixtures thereof with water. The most preferred solvent is a mixture of water and a lower alcohol such as isopropanol. The solution of perfluorocarbon copolymer has an elevated temperature below the critical temperature of the solvent in a closed vessel, typically 180 ° C to 300 ° C.
Form at 0 ° C. and elevated pressure. These solutions are miscible with solvents or diluents for perfluorocarbon copolymers such as isopropanol, ethanol, water or the like without precipitating the perfluorocarbon copolymer. It is a requirement that the solution completely enter the pores of the membrane.

The concentration of the perfluorocarbon copolymer in the solution should be high enough to cause binding of the copolymer to the membrane substrate and prevent dewetting of the resulting surface-modified membrane, but it does. It should be low enough to prevent unfavorable deterioration of the bundle properties of the surface-modified membrane. The concentration of the perfluorocarbon copolymer in the solution is typically about 0.01 wt% to about 10 wt%, more usually about 0.1 wt% to about 5 wt%.

The porous membrane substrate is a thin polymeric microporous or ultrafiltration membrane formed from a polymer composition that is not solvated or degraded by the solvent for the perfluorocarbon copolymer composition. Typical membrane pore sizes range from 10 microns to 0.01
Within the micron range. The membrane substrate is a flat sheet,
It may have any convenient geometry, including corrugated sheets, hollow fibers or the like. The membrane can be supported or unsupported, isotropic or anisotropic, skinned or unskinned, or a composite membrane. The membrane substrate has a thickness of about 5 to about 25.
It has 0 micron, preferably from about 10 micron to about 200 micron. Since the membrane is thin, this facilitates removal of unbound perfluorocarbon copolymer composition. Representative suitable membrane substrates include polyolefins such as polyethylene, polypropylene and polymethylpentene, polysulfones, polyether sulfones, polyimides, polyamides, fluorine containing polymers such as polytetrafluoroethylene, fluorinated ethylene- Examples thereof include a propylene copolymer, an ethylene-tetrafluoroethylene copolymer and a perfluoroalkoxy polymer. Preferred membrane substrates are fluorine-containing polymers, especially the polymers commonly known as fluorocarbons sold by DuPont under the trade names "Teflon® PTFE", "Teflon FEP" and "Teflon PFA". Formed from polytetrafluoroethylene, fluorinated ethylene-propylene copolymers or perfluoroalkoxy polymers such as the group.

The membrane is completely modified on all its surfaces with the bound perfluorocarbon copolymer composition, so that there are no exposed substrate surfaces. This fully modified surface is preferably substantially homogeneously coated with the bound perfluorocarbon copolymer composition. Complete surface modification prevents dewetting of the membrane when filtering the liquid. Uniform surface modification promotes uniform filtration through the filter. in addition,
The surface modifying composition is used in an amount and concentration such that the porous membrane substrate is not substantially closed or occluded as determined by measuring the increase in pressure drop across the membrane during filtration of purified water. . The modified porous membrane product of the present invention has substantially the same permeability as the unmodified porous membrane substrate as measured by pressure drop. That is, this pressure drop for the modified porous membranes of the present invention, when compared to the pressure drop across the unmodified porous membrane substrate, does not exceed a large increase by 25% birds. Preferably, this increase in pressure drop does not exceed 15% compared to the pressure drop across the unmodified porous membrane substrate, most preferably 10%.
Not exceed%.

In one embodiment of the invention, a surface modified membrane having an average pore size of 0.2 microns or less is formed. The membrane is a fluorine-containing polymer membrane substrate, the surface of which has been modified with the bonding surface modifying composition described above, preferably polytetrafluoroethylene, a fluorinated ethylene-propylene copolymer or a perfluoroalkoxy polymer. It is formed from a film substrate. The surface of the membrane substrate is completely modified by the bonding surface modifying composition. The bonded surface modifying composition prevents dewetting of the membrane during its use in filtering the liquid composition. During filtration, the "final" pressure drop across the denaturing membrane is no more than about 3 times the "initial" pressure drop across the surface denaturing membrane, preferably about 2 Not bigger than twice.

Filter pressure drop is a measure of the filter's resistance to liquid flow. A high pressure drop indicates high resistance, such as when the filter is dewetting or clogged. The low pressure drop indicates low resistance, such as when the filter is new and completely wet. In most cases, pressure drop data should be considered in comparison to the same filter under different conditions, other filters of the same type, or the same filter before surface modification. This is because different types of filters will have different pressure drops due to different membrane pore size, surface area and geometry in the filter.
Pressure drop is 1.0 gallons per minute (gpm) (3.8 liters /
Standardized with a constant liquid flow rate of
i) Measure the pressure difference across the filter. Most preferably, the pressure drop is measured with purified water during the test. The degree of pore blockage in the modified membrane, if any, is described above.

The Standard Dewetting Test is used as a means to predict the extent of dewetting or non-dewetting performance of a filter during actual filtration application. In this test, water is used as the liquid to be filtered. This test eliminates other potential flow reduction effects, such as by viscous differences in the liquid or by increased flow resistance caused by particles that can be removed from the liquid and become trapped on the membrane surface. To do. To carry out the test, the filter is moistened with 100% isopropanol,
The alcohol is drained dry and placed in a flushing device, where the filter is flushed with water by passing it through it for 10 minutes at a flow rate of 1 gallon / minute or gpm. At the end of this flushing period, the "initial" pressure drop across the filter is measured. The filter is then removed from the flushing device, drained avoiding drying of the filter and repositioned in the flushing device, where the filter is flushed with water at 1 gpm while measuring the "Drain # 1" pressure drop. . Care is taken to vent most of the air from the upstream side of the filter while initiating the flow of water through the filter.
Repeat 3 additional identical drain operations, with corresponding "Drain # 2, Drain # 3 and Drain # 4" pressure drops. After "Drain # 4" pressure drop, the filter was removed from the flushing device, drained avoiding drying of the filter, and repositioned in the flushing device, where the filter was 5 psi (34.4 kPa) across the filter.
The upstream side is pressurized with air so as to generate a pressure difference. The filter is then flushed with water at 1 gpm and the "Drain # 5, 5 psi air" pressure drop is measured. 5p
The same two additional drain operations as the si air pressurization step are repeated, with corresponding "Drain # 6, 5 psi air" and "Drain # 7, 5 psi air" pressure drops. “Drain #
The final pressure drop data corresponding to a 7.5 psi air "pressure drop is commonly referred to as the" final "pressure drop.

Also, the bonding surface modifying composition may, unless the membrane is exposed for a long enough time to cause drying of the membrane,
Prevents dewetting of the membrane during exposure of the membrane to gases such as air. During use in the filtration process, the filter can be exposed to air under a small pressure differential across the filter, such as while displacing the liquid to be filtered.

It was also found that the water bubble point pressure test can be used to predict the degree of dewetting observed on the filter during exposure to air. The lower the water bubble point pressure of the membrane, the more likely it is to dewet upon exposure to air.
On the contrary, the higher the water bubble point pressure, the lower the possibility of dewetting. The water bubble pressure of the membrane product of the present invention is at least about 50% greater than the water bubble point pressure of the unmodified membrane substrate, preferably at least about 100% greater, as measured by the water bubble point pressure test method. The water bubble point pressure test method measures the pressure required to force air through the pores of a membrane previously filled with water. The bubble point of the membrane is measured from the pressure required to displace water from the water-wet membrane. The fluid wetting membrane will allow air to pass when the applied air pressure exceeds the capillary suction of fluid into the pores. The relationship between the size of a fluid-wet cylindrical pore and the air pressure required to empty it (P, bubble point pressure of that cylindrical pore) is D = 4γ cos θ / P [where D is Is the diameter of the pore, θ is the contact angle,
And γ is the surface tension of the wetting liquid]. When the measured bubble pressure can be empirically correlated to the true membrane pore size, it is an easily obtained approximation of the true non-cylindrical pore size. One experimental method used to correlate bubble pressure with the pore size of the membranes of the present invention is to determine the smallest particles retained by the membrane. The membrane is challenged with submicron-sized latex beads and the fraction of beads retained by the membrane is measured. The maximum pores are smaller than the average diameter of the latex beads when substantially all (> 90%) of the beads are retained by the membrane.

Surface modified membranes produced in accordance with the present invention typically include
Significant improvement compared to a membrane substrate with an unmodified surface as measured by a modified SEMATECH particle retention method described in Millipore Corporation Technical Document MA041 available from Millipore Corporation of Bedford, Mass., USA It was found to have good particle retention properties. Surprisingly, the particle retention properties of the surface modified membranes are substantially improved as measured by pressure drop without significantly reducing the bundle properties of the membranes as compared to the unmodified membrane substrate. The membrane is a fluorine-containing polymer membrane substrate whose surface has been modified with the above-described composition for modifying a binding surface, preferably polytetrafluoroethylene, fluorinated ethylene-
Formed from a propylene copolymer or perfluoroalkoxy polymer film substrate.

The surface-modified membrane of the present invention comprises contacting the entire surface of a porous membrane substrate with a solution of the above-described perfluorocarbon copolymer composition under conditions such that the substrate surface is wet with the solution. Formed by. The liquid solution may inherently wet the surface of the membrane substrate, or the surface of the membrane substrate may be pre-wet with a wetting agent such as methanol, ethanol, isopropanol or acetone and then contacted with the solution, or The solution can enter the pores under pressure. Contact between the membrane substrate and the solution can be made by dipping, by passing the solution through the membrane under differential pressure, or by penetration. The perfluorocarbon copolymer composition becomes bound to the substrate surface and completely modifies the contacted substrate surface.

The membrane substrate is removed from contact with the solution and a key process step of the present invention is to mechanically remove excess modifying composition from the substrate and to cause modification on the entire substrate surface. Apply force. After contact with the solution, the membrane is positioned by interposing a flexible film between the modified membrane and a source of mechanical force, or by positioning the membrane between two non-porous polymer films to form a sandwich. Can be processed directly or indirectly. Mechanical force is applied to a single roller under pressure on one side of the membrane or sandwich, two rollers forming a nip through which the membrane or sandwich is passed, an air knife, a doctor knife, contact with an absorbent or similar Can be added appropriately. In another embodiment of the present invention, the mechanically-forced membrane further comprises an excess or unbound solvated perfluorocarbon copolymer composition such as isopropanol, ethanol, methanol, water or mixtures thereof. It is contacted with a liquid composition which is a solvent, diluent or dispersant for.
The liquid composition is also typically miscible with the solvent used to make the solution of the perfluorocarbon copolymer composition. Water can be used when it is miscible with the solvent for the perfluorocarbon copolymer composition used in the substrate surface modification step, such as alcohol. The liquid composition preferably comprises the solvent used to make a solution of the perfluorocarbon copolymer composition such as isopropanol, ethanol, water or mixtures thereof. In this step, the liquid composition further removes excess and unbound perfluorocarbon copolymer composition that may be present after applying mechanical forces, such as by dilution and / or solvation. . This further removal of unbound composition further reduces pore blockage and further removes potential extractables that may contaminate the fluid being filtered while using the surface modified membrane. Surprisingly, the liquid composition does not remove the bound perfluorocarbon copolymer composition, so the surface modification is not adversely affected by contact with the liquid composition. Optionally, a surface modified film,
Then, when the liquid composition is not water, it is contacted with water to remove the liquid composition.

The surface modified membrane is dried to remove solvent, diluent or dispersant or optionally water or liquid composition from the modification step after the application of mechanical force, and with the bound perfluorocarbon copolymer composition. Heat treatment is performed to improve the bond strength with the membrane substrate. This drying and heat treatment can be performed in a single step. The heat treatment is performed at a temperature that does not deteriorate the film substrate or the surface modifying composition. Generally, heat treatment will be from about 50 ° C to about 180 ° C, more usually from about 80 ° C to about 140 ° C.
About 5 minutes to about 72 hours at a temperature of ℃, more usually about 15
Run from minutes to about 24 hours.

The surface modified membranes produced by the process of the present invention are particularly useful for filtering gas generating liquids by preventing dewetting of the membrane used by the surface modifying composition bound to the membrane substrate. . Thus, the membrane of the present invention is
When a fluorocarbon polymer such as polytetrafluoroethylene, a fluorinated ethylene-propylene copolymer or a perfluoroalkoxy polymer is used as the substrate, an acid or base such as an acid or a base which can contain an oxidizing agent is used. It is particularly useful for filtering chemically active gas generating liquids. In these cases, both the membrane substrate and the surface modifying composition are highly resistant to chemical degradation, and the resulting surface modified membrane is not dewet by the gas.

In one embodiment of the invention, the surface-modified membrane can be wetted directly with water or the process fluid to be filtered, with or without pressure, or the membrane is first wetted with an alcohol such as isopropanol. And can be indirectly wetted. In the latter case, the alcohol is replaced by introducing water until the alcohol is removed by water and replaced, and then the process fluid to be filtered is introduced. The water containing filtration device containing the water-wet surface modified membrane of the present invention is then sealed in a container, if desired, with additional water and by steam sterilization to inactivate the microorganisms therein. And so on.
For example, the method disclosed in U.S. Pat.No. 4,727,705 can be used to form a water wet filtration device that can be transported to an end user, which then
Such a filtration device can be used directly without having to carry out a membrane wetting process.

Examples The following examples illustrate the invention and are not intended to limit the invention.

Example 1 A solution was prepared containing 0.5% by weight of the trade name "Nafion" perfluorocarbon copolymer in a mixture of lower aliphatic alcohol and water. This is a 5 wt% "Nafion" perfluorocarbon copolymer solution in a mixture of commercially available lower alcohol and water available from Aldrich Chemical Company, Inc., Milwaukee, WI, USA, with isopropyl alcohol.
It was made by diluting 10: 1. "Nafi in solution
The "on" perfluorocarbon copolymer was in the sulfuric acid form and had an average equivalent weight of 1,100.

Containing a polytetrafluoroethylene (PTFE) membrane with a pore size of 0.1 micron in a container with a dilute solution of "Nafion" perfluorocarbon copolymer from above 10
The inch (25 cm) pleated filter device was slowly dipped. This prevents the solution from entering the filter downstream or inside, except through the membrane, by any other means, until the level of the solution upstream or outside the filter completely covers the membrane. Carried out. The time was allowed for the solution to penetrate the membrane so that it filled the filter core downstream. 1 inch (2.5 cm) H downstream of the filter when the core is filled with solution
A pressure differential was created across the membrane by applying a vacuum of g, thus the solution began to flow through the membrane and exited the core of the filter. In addition to the volume downstream of the filter, a total of 240 milliliters of solution was passed through the filter at a slow flow rate (as dictated by a small pressure differential across the membrane). The filter is then removed from the solution, the excess solution drained, being careful to avoid drying the filter, and the first containing 100% isopropanol to remove excess perfluorocarbon copolymer from the membrane. I put it in two containers. In addition to the volume downstream of the filter, a total of 2 liters of isopropanol was passed through the filter under the same pressure differential conditions as above. Then
The isopropanol wet filter was removed from isopropyl alcohol, drained isopropyl alcohol without drying and placed in a flushing device where it was flushed with water. This was done by passing water through the filter at a flow rate of 1 gallon / min for 20 minutes to further remove any residual unbound perfluorocarbon copolymer and / or isopropanol. The water-flushed filter was removed from the apparatus and immersed in 2 molar hydrochloric acid for 16 hours to further clean the filter. The filter was removed from the hydrochloric acid, rinsed with water, and further flushed with water for 30 minutes as previously described. The drained water wet filter was then placed in an oven and the filter was dried and exposed to heat of 120 ° C. for 16 hours to improve the bond strength between the bonded perfluorocarbon copolymer and the membrane substrate. .

Dry denaturing filter with 60% isopropanol / 40
% Water, and tested for integrity by the bubble point pressure test method. The bubble point pressure of the filter was measured to be 42 psi, indicating the filter was integral. The filter was then wetted with 100% isopropanol, drained, and attached to a flushing device where the filter was flushed with water at a flow rate of 1 gal / min for 5 minutes to replace the isopropanol. The pressure drop across the filter is measured to be 0.66 psi / gpm
(1.20 kPa / liter / minute). The pressure drop of the same type of unmodified wet PTFE filter was measured under the same conditions and was 0.65 psi / gpm (1.18 kPa / l / min).

Example 2 Approximately 100 lines (30
cm) feet of continuous length were surface modified with "Nafion" perfluorocarbon copolymer. This is 5 feet per minute (1.5 m / min) of the membrane across a bath containing a solution containing 5 wt% "Nafion" perfluorocarbon copolymer of Example 1.
Min) for a total contact time of about 2 minutes. The membrane was then sent to a second bath containing water to remove excess solution from the membrane. The contact time between the membrane and water in this bath was about 5 minutes. The membrane was then sent to a third bath where fresh water was constantly sprayed onto the membrane to further purify the membrane. The contact time between the membrane and water in this bath is about 5
It was a minute. The wet modified membrane was then passed under hot air to dry the membrane. The dried film was then rolled up to form a roll. The modified membrane roll was placed in a furnace at 100 ° C. for 16 hours to improve the bond strength between the bonded perfluorocarbon copolymer and the film substrate.

A 4 inch (10 cm) pleated filter device was made using the surface modified membrane. This was done by heat sealing the membrane to a perfluoroalkoxy polymer housing. The device was found to be integral when tested by the bubble point pressure method. The pressure drop across the filter is measured to be 1.5 psi / gpm (2.72 kPa / liter /
Minutes). The pressure drop of the same type of filter device was measured under the same conditions except that it contained a native wet PTFE membrane and was found to be 1.5 psi / gpm.

Example 3 A 47 mm diameter disk of PTFE membrane with 0.1 micron pore size was immersed in the 5 wt% "Nefion" perfluorocarbon copolymer solution from Example 1 for 2 minutes. The membrane disc was removed from the solution and the excess solution drained, taking care not to let it dry. The wet membrane was then immersed in 10 milliliters of 100% isopropanol for 5 minutes to remove excess perfluorocarbon copolymer, followed by three water rinses to replace the isopropanol. The water-wet film was placed in an oven and dried at 120 ° C for 2 hours. The surface modified membrane is based on the weight of the initial membrane substrate, with the bound perfluorocarbon copolymer attached 3.
It was found to have an increase of 7% by weight.

Used to remove excess copolymer from modified membranes 10
Milliliters of 100% isopropanol were concentrated to 1 ml by evaporation and analyzed by Fourier Transform Infrared Spectroscopy (FTIR). The FTIR spectrum of the concentrate showed the presence of perfluorocarbon copolymer, demonstrating that unbound perfluorocarbon copolymer was removed from the membrane by solvation and / or dilution. The FTIR spectrum of the isopropanol blank showed no evidence of perfluorocarbon copolymer.

Example 4 10 ml of dried surface modified membrane from Example 3
Immersion in 0% isopropanol for 5 minutes, followed by 3 water rinses to replace the isopropanol and drying in an oven at 120 ° C. for 2 hours. The weight of the modified membrane disc was found to be the same as the weight of the membrane before exposure to isopropanol in this example (weight of modified membrane of Example 3). This example showed that when the modified membrane was heat treated during or after the drying step in Example 3, it was deposited even after contacting the membrane with a solvent or diluent for solvated unbonded perfluorocarbon copolymer. It illustrates that all of the bound perfluorocarbon copolymer remains on the membrane surface.

(Comparative) Example 5 P with a pore size of 0.1 micron according to the method of Example 3
A 47 mm diameter disk of TFE membrane was surface treated with "Nafion" perfluorocarbon copolymer. However, the membrane was not exposed to heat during the drying process. Instead, the membrane is 2 at room temperature.
Allowed to dry for hours. The surface modified membrane was found to have a 4.1 wt% increase based on the weight of the initial membrane substrate due to the attached perfluorocarbon copolymer attached.

Then dry the surface-modified membrane with 10 ml of 100
% Isopropyl alcohol for 5 minutes, then rinsed 3 times with water to replace the isopropanol and dried for 2 hours at room temperature. The membrane disc was found to have a weight loss equivalent to 7.4% by weight, based on the weight of attached bound perfluorocarbon copolymer present prior to exposing the dry modified membrane to isopropanol. . Although this example shows that the modified membrane retains most of the attached perfluorocarbon copolymer deposited on the membrane surface after contact with the solvent or diluent for the unbound solvated perfluorocarbon copolymer. , Demonstrating that if the film is not heat treated during or after the drying step, small amounts can be removed.

Example 6 P with 0.1 micron pore size according to the procedure of Example 1
A 10-inch pleated filter device containing TFE membrane is installed
Modified with "n" perfluorocarbon copolymer. Also,
A similar filter containing a 0.05 micron membrane was surface modified in the same manner. After wetting both filters with water, 2
One water wet filter was sealed in a bag containing water and sterilized under autoclaved conditions. Allow the bag containing the wet filter to cool for 24 hours, then
The filter was removed from the bag and the pressure drop was measured. The 0.1 micron filter had a pressure drop of 0.8 psi / gpm (1.45 kPa / liter / min) and the 0.1 micron filter had a pressure drop of 1.0 psi / gpm (1.82 kPa / liter / min).

The two filters were then wetted with 100% isopropanol and flushed with water to determine the pressure drop after the rewetting operation. 0.1 micron filter is 0.8 psi /
It had a pressure drop of gpm and the 0.05 micron filter had a pressure drop of 1.0 psi / gpm. This example illustrates the non-dewetting properties of the products of this invention under highly gassing liquid conditions.

(Comparative) Example 7 Paul of East Hills, NY, USA
From Corporation, a water-wet "Super-" containing a 0.1 micron pore size PTFE membrane sealed in a bag containing water.
The Cheminert "(R) filter device was obtained.
Similarly, a 0.05 micron pore size PT from Paul Corporation, East Hills, NY, USA
A water-wet "Ulti-Cheminert" (trade name) filter device containing an FE membrane was also obtained. The pressure drop across the two “as received” filters was measured immediately after removing the filters from the corresponding bags. 0.1 psi / 1.4 psi /
It has a pressure drop of gpm (2.54 kPa / liter / min), and a 0.05 micron device is 6.3 psi / gpm (11.4 kPa / liter / min).
Min) pressure drop.

The two filters were then wetted with 100% isopropanol and flushed with water to determine the pressure drop after the rewetting operation. 0.7 psi / gpm for 0.1 micron equipment
Has a pressure drop of (1.27 kPa / l / min) and 0.
05 micron equipment is 0.9psi / gpm (1.63kPa / l / min)
Had a pressure drop of. This example illustrates that the dewetting phenomenon is observed with prior art products in the presence of gas generating liquids such as water.

Example 8 A 47 mm diameter disk of ultra-high molecular weight polyethylene membrane with a pore size of 0.1 micron was prepared from 5% by weight from Example 1 "Nafio
It was immersed in the "n" perfluorocarbon copolymer solution for 2 minutes. The membrane disc was removed from the solution and the excess solution drained, taking care not to let it dry. The wet membrane was then immersed in 10 milliliters of 100% isopropanol for 5 minutes to remove excess perfluorocarbon copolymer and then rinsed 3 times with water to replace the isopropanol. The water-wet film was placed in an oven and dried at 90 ° C for 2 hours. The surface modified membrane was found to have an increase of 2.8 wt% based on the weight of the initial membrane substrate due to the attached perfluorocarbon copolymer attached. The presence of the perfluorocarbon copolymer on the surface of the modified membrane was confirmed by FTIR analysis.

Example 9 A 10 inch laminated disc filter device containing a PTFE membrane with 0.1 micron pore size was modified with "Nafion" perfluorocarbon copolymer as described in Example 1. The modified filter was tested according to the modified SEMATECH particle retention method described above and found to have a Log Reduction Value of 4.5 at 0.05 micron particles.
(LRV) (retention rate 99.995%).
The pressure drop across the filter is measured to be 0.77 psi / gpm (1.4
It was 0 kPa / liter / minute).

We also modified a native control filter of the same type with SEMA
When tested according to the TECH particle retention method, it was found to have a Log Reduction Value (LRV) of 1.0 (retention rate 90.0%) at 0.05 micron particles. When the pressure drop of the filter is measured, it is 0.74psi / gpm (1.34kPa / liter /
Minutes). This example illustrates the improved particle retention properties of the products of the invention.

Example 10 The following filter according to the standard dewetting test described above: (1) PTFE with a pore size of 0.05 micron.
A 10 inch pleated filter device comprising a membrane, the surface of which was modified with "Nafion" perfluorocarbon copolymer according to Example 1, (2) the same PTFE type unmodified wet control filter, and (3 ) "Ultra-C containing 0.05 micron pore size PTFE membrane obtained from Pall Corporation of East Hills, NY
The "heminert" filter device, was tested.

The test results are presented in FIG. 3, which represents a plot of pressure drop versus condition or drain number. Denaturing filter (1)
Shows a 64% increase in pressure drop from the initial pressure drop during filtration, whereas filters (2) and (3) show 600% and 300% increase from the initial pressure drop during filtration, respectively.
% Increase. Then all filters are 100%
Rewet with isopropanol and water pressure drop was measured again. After the rewet operation, the pressure drops were all substantially the same as the initial pressure drop, which means that the observed increase in pressure drop or loss of bundle properties during the test resulted in dewetting during the filtration process. It was due only to.

Example 11 A 10 inch pleated disc filter device containing a PTFE membrane with a pore size of 0.05 microns was modified with "Nafion" perfluorocarbon copolymer as described in Example 1. Then filter the “Standard SC2 Drain Tes
It was tested according to the t "method as follows.
Wet with% isopropanol and flush with water to replace the alcohol. The filter was then mounted on the filter holder of the recirculation chemical bath system filtration system used to purify the liquid bath used to clean the silicon wafer during the manufacture of the integrated circuit. This liquid, known as SC2, contains 0.2 parts of 37% hydrochloric acid (HCl),
It is a highly gas-generating, chemically active liquid containing 1 part of 30% hydrogen peroxide (H ₂ O ₂ ) as a strong oxidant, and 5 parts of water. The temperature of the liquid in the bath is maintained at 80 ° C.

A positive displacement pump is used to propel the liquid through the filter device during the filtration process, thus creating a pressure drop across the filter. Since direct pressure drop data for the filter is difficult to obtain during use, the pressure upstream of the filter (P) as well as the fluid flow rate (Q) through the filter is monitored. It is common practice in industry to use the ratio of the above pressure divided by the flow rate (P / Q) as an indicator of total system resistance to flow. The P / Q ratio is a measure of the resistance of the filter to liquid flow, since the only part of the filtration system that can potentially change over time is the filter's resistance to flow due to particulate removal or by dewetting. It is a direct measure.
P / Q ratio is a more sensitive measure of the flow resistance of a filter. Because it changes significantly more than P or Q alone. P is measured in pounds per square inch (psi) and Q is measured in gallons per minute (gpm). Therefore, the P / Q ratio is given in units of psi / gpm. If necessary, this process is explained in more detail. See Millipore Corporation Technical Document MA059, available from Millipore Corporation of Bedford, Massachusetts, USA.

The SC2 liquid was filtered at 80 ° C. using a wet filter attached to the holder of the filtration system and the “initial” P and Q were measured. In this example, we use only clean SC2 liquid and avoid other potential effects that may result in increased resistance to liquid flow, such as retention of particles and thus wafers to isolate the dewetting phenomenon. Was not processed. Use a pump to expel liquid from the filter holder through the drain valve and vent valve, and propel air through the system, including the filter holder, to remove liquid in the bath from the bath and tubing (including pump). The entire volume was also discharged. After this first drain cycle, the bath is flushed with fresh SC while the liquid is flowing through the filter.
Filled with 2 liquids and heated to 80 ° C. Liquid temperature 80
After being brought to ° C, the "Drain # 1" P and Q values were measured. This drain cycle was repeated 5 more times, and after each drain cycle its corresponding P and Q values were measured.
For comparison, "Ulti-Ch" containing an unmodified wet control filter containing 0.05 micron PTFE membrane (Filter 2) and a 0.05 micron pore size PTFE membrane obtained from Pall Corporation of East Hills, NY, USA.
This example was repeated using the "eminert" filter (filter 3).

The results from this example are presented in Figure 2, which represents a plot of P / Q ratio vs. drain number. The results show that the modified membrane filter (filter 1) produced according to the present invention shows that these extremely chemically aggressive and highly outgassing gases are evidenced by a constant P / Q ratio over time or drain number. It does not dehumidify even under sexual conditions, whereas the native filter (filter 2) and the "Ulti-Cheminert" filter (filter 3)
Dewetting has been shown, as can be seen by increasing the / Q ratio.

Example 12 A 10 inch laminated disc filter device containing a PTFE membrane having a pore size of 0.1 micron was modified with "Nafion" perfluorocarbon copolymer as described in Example 1. Moisten the filter with 100% isopropanol,
Then, it was flushed with water to replace the alcohol. 0.
A similar filter containing a modified PTFE membrane with a pore size of 05 microns was wetted in the same manner. Two water wetting filters were attached to the bubble point pressure tester and the water bubble point pressure of the filters was measured. In the same manner, the water bubble point pressure of the unmodified wet control filter was also measured.

The bubble point pressure of the two denaturing filters is 40 psi (275 kP
The bubble point pressure of the native filter was lower than 5 psi (3.4 kPa).

Example 13 Some samples of 0.1 micron pore PTFE membrane modified with "Nafion" perfluorocarbon copolymer according to the methods of Examples 1 and 3 were wetted with 100% isopropanol and rinsed with water to replace the alcohol. did. The water wet sample was immersed in the following chemicals under the following conditions:

(A) 97% sulfuric acid, 150 ° C, 100 hours (b) 30% hydrogen peroxide, 50 ° C, 100 hours (c) 2.4% tetramethylammonium hydroxide, 5
0 ° C, 100 hours (d) SC1 solution containing 1 part ammonium hydroxide (28%), 1 part hydrogen peroxide (30%) and 5 parts water, 80
℃, 3 hours (e) 1 part hydrochloric acid (37%), 1 part hydrogen peroxide (30%)
And SC2 solution containing 5 parts water, 80 ° C., 3 hours (f) 7 parts sulfuric acid (97%) and 1 part hydrogen peroxide (30
%) Containing piranha solution, 135 ° C., 168
Time SC1 and SC2 solutions were replaced with fresh solution every 30 minutes at temperatures that maintained effective oxidant levels, and piranha solution was replaced with fresh solution every 24 hours. Furthermore,
The samples from (c) and (d) were tested and then treated with hydrochloric acid to ensure that all samples were in the acid form after testing.

After exposure to these highly aggressive chemicals, the samples were rinsed thoroughly with water, after which they were analyzed by FTIR with control samples that were not exposed to the chemicals. The FTIR spectra of all samples, including the control, were the same, indicating that no changes in the chemical composition of the modified membrane occurred. In addition, quantitative analysis of FTIR spectra determined that no change in the amount of modifying perfluorocarbon composition occurred.

Comparative Example 14 This example illustrates the prior art method described in U.S. Pat. No. 4,470,859 and the undesirable results obtained thereby. The degree of surface modification of the porous membrane substrate with the perfluorocarbon copolymer composition was determined by dyeing with a dye according to the procedure described below.

First, 8 inch x 10 inch (20 cm x 2) of "Nafion 117"
Cut 5cm film to 2 inch x 2 inch (5cm x 5c
m) The product name "Nafion 1
A solution of 17 "perfluorocarbon copolymer was made. The trade name "Nafion 117" is the sulfonic acid form of the "Nafion" copolymer film with an ion exchange capacity of 0.91 meq / g and an equivalent weight of 1100.

The smaller piece of film was then converted to the lithium sulfonate form of the copolymer. This was done by immersing them in an aqueous solution of 3 wt% LiOH and 1 wt% dimethylsulfoxide (DMSO) based on the weight of the solution. The solution was heated to 50 ° C. for 4 hours and then cooled to room temperature. Film strips were removed from the solution and rinsed 3 times in 1 hour in deionized water. The film pieces were measured to contain the perfluorocarbon copolymer in the lithium sulfonate form.

285 ml of 15 g piece of lithium modified film in a round bottom flask
With tetramethylene sulfone (sulfolane) solvent and 240 ° C with stirring under a nitrogen blanket.
Heated for 4 hours. The solution was then cooled to 25-30 ° C. to form a 5 wt% solution of the copolymer, which was diluted by adding sulfolane to form a 1 wt% solution.

Following the procedure of US Pat. No. 4,470,859, a 2 micron PTFE membrane was then dipped into a 1% solution, which did not wet the membrane. The vessel containing the solution and the membrane was placed in a vacuum chamber and a vacuum of 150 mm Hg absolute was applied for 2 minutes and then rapidly vented to atmosphere. The vacuum and rapid venting were repeated. The solution did not wet the membrane.

The membrane was then removed from the solution and placed in an oven at 130 ° C for 6 hours. The membrane was removed from the oven, cooled at room temperature, and immersed in isopropanol (IPA) to wet the membrane. Then wet the membrane with 0.1% of methylene blue dye.
The film was immersed in an aqueous solution until the film surface was dyed. Then, with stirring to remove excess dye from the membrane,
The membrane was washed sequentially in water, IPA and water. Then
The membrane was stained.

The drawing in FIG. 7 shows that the surface modifying composition incompletely modified the membrane surface, as indicated by the dark spots. The light background consists of an unmodified membrane substrate. Figure 3 (unstained
A control of PTFE membrane) and FIG. 4 (PTFE soaked in 0.1% aqueous solution of methylene blue and then rinsed) shows that the PTFE membrane substrate is not stained by methylene blue.

The surface modification method of the 0.2 micron PTFE porous membrane of U.S. Pat. Pre-wet for 10 seconds. IPA immediately PTFE
Wet the substrate. In addition, contact was not made by vacuum and degassing. The membrane was pre-wet. The purpose of the pre-wetting step was to investigate if it improved the surface modification results shown in FIG.

After pre-wetting with IPA, the membrane was immersed in sulfolane for 5 minutes to replace IPA in the membrane with sulfolane. The sulfolane-wet membrane was then immersed in a 1% sulfolane solution of the perfluorocarbon copolymer composition for 5 minutes. The membrane was then removed from the solution and immersed in a fresh 1% sulfolane solution of the perfluorocarbon copolymer composition for 15 minutes.

The membrane was then removed from the solution and oven dried at 130 ° C for 6 hours. The surface modified membrane was then stained with methylene blue as previously described in this example. The surface modified membrane is shown in the drawing of FIG. As shown in FIG. 8, PT
The FE membrane is incompletely surface modified.

Comparative Example 15 This example illustrates that the use of the prior art method described in US Pat. No. 4,470,859 and the copolymer precipitation technique to surface modify membranes gives unsatisfactory results.

A 0.2 micron PTFE membrane substrate was immersed in the 1% sulfolane solution of Example 14 and vacuum and rapid degassing were performed in two cycles as described in Example 14. The solution did not wet the membrane. The membrane was removed from the solution and immersed in toluene for 15 seconds to cause precipitation of the perfluorocarbon copolymer composition. The membrane was then removed from the toluene and placed in a furnace at 130 ° C for 6 hours. The membrane was removed from the oven, cooled and stained with methylene blue by the procedure described in Example 14.

The surface of the obtained membrane shown in FIG. 5 is incompletely modified.

The surface modification method of the 0.2 micron PTFE porous membrane of US Pat. The membrane was pre-wet with IPA by dipping it in IPA. In addition, contact could not be made by vacuum and degassing. The membrane was pre-wet. The purpose of the pre-wetting process is to
It was to see if it improved the surface modification results shown in FIG.

After pre-wetting with IPA, the membrane was immersed in sulfolane for 5 minutes to replace IPA in the membrane with sulfolane. Then
The membranes wetted with sulfolane were immersed in a 1% sulfolane solution of the perfluorocarbon copolymer composition of Example 14 for 5 minutes. The membrane was then removed from the solution and immersed in a fresh 1% sulfolane solution of the perfluorocarbon copolymer composition of Example 14 for 15 minutes. The membrane was removed from the solution and immersed in toluene for 15 seconds to cause precipitation of the perfluorocarbon copolymer composition. The membrane was removed from toluene and oven dried at 130 ° C for 6 hours.
The surface modified membrane was then stained with methylene blue as described in Example 14. The surface treatment film is shown in FIG. The membrane is shown in FIG.
Although more of its surface is modified with the copolymer as compared to the membrane shown in, the surface is incompletely modified, which is undesirable.

Example 16 This example illustrates the method of the present invention when using a perfluorocarbon copolymer solution formed with a solvent that wets the membrane.

The sulfonic acid form of Nafi, dissolved in a mixture of lower alcohol and water, obtained from Aldrich Chemical Company, Milwaukee, WI, USA.
A 0.05 micron PTFE membrane was immersed in a 1 wt% solution of the "on" perfluorocarbon copolymer for 1 minute at room temperature. The membrane wets immediately in solution. This perfluorocarbon copolymer had an equivalent weight of 1100.

The membrane was removed from the solution and placed between two thin non-porous polyethylene sheets to form a sandwich, which was placed on a flat surface. Excess solution was removed from the sandwich by rolling a pressure roller across the exposed surface of the sandwich. The membrane was removed from the sandwich and oven dried at 120 ° C for 2 hours.

The membrane was removed from the oven, cooled to room temperature, and immersed in IPA to wet the membrane. The membrane was removed from the IPA and immediately immersed in a 0.1% aqueous solution of methylene blue with stirring.

The membrane was then washed in water to remove excess methylene blue, then IPA and then immersed in water.
The membrane was then dried at room temperature. The obtained film is shown in FIG. 9, and the surface of this film is completely modified with the composition for surface modification.

Example 17 This example involves contacting a membrane with a non-wetting perfluorocarbon copolymer solution and then subjecting the membrane to mechanical forces that make the concentration of the modifying composition more uniform on the membrane surface. It illustrates that a solution can be used to produce the membranes of the invention.

By the prewetting operation described in Example 15, 0.05 micron PT
The FE membrane was pre-wet with IPA. The membrane was then removed from the IPA and immersed in sulfolane for 5 minutes to replace the IPA in the membrane with sulfolane. The sulfolane-wet film was then immersed in the 1% perfluorocarbon copolymer solution described in Example 14 for 5 minutes. The membrane was then removed from the solution and soaked in a fresh 1% sulfolane solution of the perfluorocarbon copolymer composition of Example 14 for 15 minutes.

The membrane was removed from the solution and placed between two thin non-porous polyethylene sheets to form a sandwich, which was placed on a flat surface. Excess solution was removed from the sandwich by rolling a pressure roller across the exposed surface of the sandwich. The membrane was removed from the sandwich and oven dried at 120 ° C for 2 hours. The membrane was removed from the oven, cooled to room temperature and immersed in IPA to wet the membrane.

The membrane was then stained with methylene blue by the procedure described in Example 14. The film obtained is shown in FIG. The surface of the film is completely modified with the composition for surface modification.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01D 71/82 B01D 71/32 B01D 71/36

Claims (13)

(57) [Claims] 1. A fluorine-containing monomer; and (SO ₂ F), (SO ₃ M), (SO ₃ R), (SO ₂ NR ₂ ), (CO
F), (CO ₂ M), (CO ₂ R) or (CONR ₂ ) group (where M is H, alkali metal, alkaline earth metal or NR ₄ and each R is independently H, Alkyl or aryl groups, and these may optionally contain other functional groups selected from hydroxyl, amine, ether or carbonyl groups to form substituted alkyl or substituted aryl groups) In forming a thin non-wettable porous membrane product comprising a thin porous polymeric substrate having attached bound perfluorocarbon copolymer formed from a fluorine-containing monomer containing groups, said perfluorocarbon The copolymer is substantially insoluble in the solvent or diluent for the unbound perfluorocarbon copolymer, and the porous membrane product is substantially the same in water or aqueous solution as the porous polymer substrate. A method of forming a thin, non-wettable porous membrane product having permeability comprising: a) adding a solution containing a perfluorocarbon copolymer to
Contacting the polymer substrate having a thickness of microns to 250 microns and a pore size of 0.01 microns to 10 microns resulting in the deposition and bonding of a perfluorocarbon copolymer onto the polymer substrate, b). Mechanical force is applied to the polymer substrate having bound and unbound perfluorocarbon copolymer from step (a) to remove bound perfluorocarbon copolymer from the polymer substrate. Selectively removing excess unbound perfluorocarbon copolymer from the polymer substrate while substantially avoiding: c) providing the polymer substrate with the bound perfluorocarbon copolymer on the surface; Heat treating, and d) recovering said thin non-wetting porous polymeric substrate having perfluorocarbon copolymer deposited over said exposed surface, said perfluorocarbon copolymerization Is substantially insoluble in the solvent or diluent for the unbound perfluorocarbon copolymer, and said porous membrane product is a thin non-wettable porous material having substantially the same permeability as said porous polymeric substrate. Method for forming a membrane product. 2. The polymer substrate obtained from step (b) is contacted with a solvent, diluent or dispersant for unbonded perfluorocarbon copolymer prior to said heat treating step.
The method described. 3. The method according to claim 1, wherein the polymer substrate is a fluorine-containing polymer. 4. The method according to claim 3, wherein the fluorine-containing polymer is polytetrafluoroethylene. 5. The method of claim 3 wherein the fluorine containing polymer is a perfluoroalkoxy polymer. 6. The method according to claim 3, wherein the fluorine-containing polymer is a fluorinated ethylene-propylene copolymer. 7. The perfluorocarbon copolymer has the following groups: (SO ₂ F), (SO ₃ M), (SO ₃ R), (SO ₂ N).
R ₂ ), (COF), (CO ₂ M), (CO ₂ R) or (CONR ₂ ) (where M is H, alkali metal, alkaline earth metal or NR
₄ and each R is independently H, an alkyl group, an aryl group, a substituted alkyl group or a substituted aryl group)
3. A method according to any one of claims 1 or 2 containing at least one of 8. The perfluorocarbon copolymer has the following groups: (SO ₂ F), (SO ₃ M), (SO ₃ R), (SO ₂ N).
R ₂ ), (COF), (CO ₂ M), (CO ₂ R) or (CONR ₂ ) (where M is H, alkali metal, alkaline earth metal or NR
₄ and each R is independently H, an alkyl group, an aryl group, a substituted alkyl group or a substituted aryl group)
The method of claim 3, comprising at least one of: 9. The perfluorocarbon copolymer has the following groups: (SO ₂ F), (SO ₃ M), (SO ₃ R), (SO ₂ N).
R ₂ ), (COF), (CO ₂ M), (CO ₂ R) or (CONR ₂ ) (where M is H, alkali metal, alkaline earth metal or NR
₄ and each R is independently H, an alkyl group, an aryl group, a substituted alkyl group or a substituted aryl group)
The method of claim 4, comprising at least one of: 10. The perfluorocarbon copolymer has the following groups: (SO ₂ F), (SO ₃ M), (SO ₃ R), (SO ₂ N).
R ₂ ), (COF), (CO ₂ M), (CO ₂ R) or (CONR ₂ ) (where M is H, alkali metal, alkaline earth metal or NR
₄ and each R is independently H, an alkyl group, an aryl group, a substituted alkyl group or a substituted aryl group)
The method of claim 5, comprising at least one of 11. The perfluorocarbon copolymer has the following groups: (SO ₂ F), (SO ₃ M), (SO ₃ R), (SO ₂ N).
R ₂ ), (COF), (CO ₂ M), (CO ₂ R) or (CONR ₂ ) (where M is H, alkali metal, alkaline earth metal or NR
₄ and each R is independently H, an alkyl group, an aryl group, a substituted alkyl group or a substituted aryl group)
7. The method of claim 6 containing at least one of: 12. The lower alcohol solution containing a perfluorocarbon copolymer as claimed in claim 1, 2.
The method according to any one of 4, 5, or 6. 13. The method according to claim 3, wherein the solution is a lower alcohol solution containing a perfluorocarbon copolymer.